Scientists move closer to earthquake prediction
Thursday, 10 Jul 2008 10:41
Researchers measured changes at the San Andreas Fault Observatory at Depth
Scientists believe they are one step closer to creating a system that could predict when earthquakes are about to strike.
A team in the United States managed to measure changes in the speed of seismic waves that preceded two small earthquakes by ten and two hours.
Publishing the results in the journal Nature today, the researchers argue the changes are an encouraging sign that hold promise for earthquake prediction.
Over the course of two months they measured the changes using the twin boreholes of the National Science Foundation's San Andreas Fault Observatory at Depth.
Measurements including barometric pressure - a known source of stress - and changes in seismic waves.
They found that higher barometric pressure coincided with a faster seismic wave speed.
The researchers also uncovered two other wave-speed anomalies.
One in particular was the largest signal observed over the entire two-month period and was unrelated to barometric pressure changes.
"We found that this anomaly occurred at the time of the largest local event, a magnitude three earthquake, and most importantly began 10.6 hours before the event," said study co-author Paul Silver of the Carnegie Institution's department of terrestrial magnetism.
"Such pre-seismic changes are consistent with lab experiments that exhibit precursory phenomena, namely an increase in microcrack density preceding the occurrence of an earthquake.
Lead author Fenglin Niu of Rice University said the researchers are "very encouraged" by the pre-seismic signals and are planning further studies to better understand their timing and physical basis.
"Detecting a pre-seismic velocity change is at best only a small step toward reliable earthquake prediction," he added.
"Before we can supply any useful information before an earthquake, we will need a physical model that can explain when such a velocity change would occur before a quake."
